Evidence of tetrapods is scarce in the early Mississippian. Following Romer's Gap, a time of some 15 million years at the beginning of the Mississippian when remains of tetrapods and other continental organisms are rare, only sporadic skeletal and footprint fossils are found. We report here on new specimens of the tetrapod ichnogenera Hylopus and Palaeosauropus from the middle of the Mauch Chunk Formation (middle to upper Mississippian) of Eastern Pennsylvania. These document walking and swimming behaviors by at least two basal tetrapod taxa, perhaps an anthracosaur and a temnospondyl, and show evidence for the beginning of the second period of tetrapod diversification.